1. Field of the Invention
The present invention relates to an image processing device and an image processing method that perform white balance correction for adjusting the tint of an image, and a recording medium that stores an image processing program that perform white balance correction for adjusting the tint of an image.
2. Description of the Related Art
The colors of a photographed image taken with a digital camera or the like are affected by the color of light illuminating the subject, such as white light, setting sun's light, and candlelight. For example, if a subject is photographed in the light of a tungsten lamp, the resulting photographed image tends to be generally strongly red-tinged. On the other hand, a human eye can adjust the sensitivity level of the visual cells to reduce the color change of the subject to a minimum when the light source is changed. Thus, even in the light of a tungsten lamp emitting red-tinged light, the sensitivity of the cells sensitive to red light can be reduced to provide a view similar to that in the normal white light. Therefore, depending on the light source illuminating the subject, the photographed image may appear with a substantially different impression than the photographer got when he/she took the image.
In order to bring the colors of the image close to those the photographer thought he/she saw when took the image, white balance correction has to be carried out to adjust the colors of the image so that the white color in the image is always reproduced as white. Concerning the white balance correction, in patent reference 1, there is described a method of estimating the color temperature of a light source illuminating a subject based on the chromaticity of an image and performing a color adjustment process based on the estimated color temperature of the light source.
However, the chromaticity value of blue lies in a range that is determined to have high temperature. Therefore, according to the method described in the patent reference 1, the white balance correction is performed on not only the images of subjects illuminated by blue-tinged light having a high color temperature but also the images of blue subjects. As a result, there is a possibility that even images of a blue car, blue sky or the like, which require no correction, are disadvantageously corrected to be white-tinged.
Besides, even images of the same subject taken in the light of the same light source vary in chromaticity distribution depending on the type of the negative of the film, the exposure condition, the type of the camera or the like. Therefore, the method described in the patent reference 1 may cause variable precision of the white balance correction.
The term “photographed image” used herein refers to not only photographed images taken with digital cameras but also photographed images taken with film cameras, photographed images of motion pictures taken with video cameras and the like.
Patent reference 1: Japanese Patent Laid-Open No. 2000-78607